Internal Error triggered by vectorization

[TH3CHARLie]

Repro code, generated using fuzzing on bilateral_grid app

#include "Halide.h"

using namespace Halide;

int main(int argc, char **argv) {
    ImageParam input(Float(32), 2, "input");
    const float r_sigma = 0.1;
    const int s_sigma = 8;
    Func bilateral_grid{"bilateral_grid"};

    Var x("x"), y("y"), z("z"), c("c");

    // Add a boundary condition
    Func clamped = Halide::BoundaryConditions::repeat_edge(input);

    // Construct the bilateral grid
    RDom r(0, s_sigma, 0, s_sigma);
    Expr val = clamped(x * s_sigma + r.x - s_sigma / 2, y * s_sigma + r.y - s_sigma / 2);
    val = clamp(val, 0.0f, 1.0f);

    Expr zi = cast<int>(val * (1.0f / r_sigma) + 0.5f);

    Func histogram("histogram");
    histogram(x, y, z, c) = 0.0f;
    histogram(x, y, zi, c) += mux(c, {val, 1.0f});

    // Blur the grid using a five-tap filter
    Func blurx("blurx"), blury("blury"), blurz("blurz");
    blurz(x, y, z, c) = (histogram(x, y, z - 2, c) +
                            histogram(x, y, z - 1, c) * 4 +
                            histogram(x, y, z, c) * 6 +
                            histogram(x, y, z + 1, c) * 4 +
                            histogram(x, y, z + 2, c));
    blurx(x, y, z, c) = (blurz(x - 2, y, z, c) +
                            blurz(x - 1, y, z, c) * 4 +
                            blurz(x, y, z, c) * 6 +
                            blurz(x + 1, y, z, c) * 4 +
                            blurz(x + 2, y, z, c));
    blury(x, y, z, c) = (blurx(x, y - 2, z, c) +
                            blurx(x, y - 1, z, c) * 4 +
                            blurx(x, y, z, c) * 6 +
                            blurx(x, y + 1, z, c) * 4 +
                            blurx(x, y + 2, z, c));

    // Take trilinear samples to compute the output
    val = clamp(input(x, y), 0.0f, 1.0f);
    Expr zv = val * (1.0f / r_sigma);
    zi = cast<int>(zv);
    Expr zf = zv - zi;
    Expr xf = cast<float>(x % s_sigma) / s_sigma;
    Expr yf = cast<float>(y % s_sigma) / s_sigma;
    Expr xi = x / s_sigma;
    Expr yi = y / s_sigma;
    Func interpolated("interpolated");
    interpolated(x, y, c) =
        lerp(lerp(lerp(blury(xi, yi, zi, c), blury(xi + 1, yi, zi, c), xf),
                    lerp(blury(xi, yi + 1, zi, c), blury(xi + 1, yi + 1, zi, c), xf), yf),
                lerp(lerp(blury(xi, yi, zi + 1, c), blury(xi + 1, yi, zi + 1, c), xf),
                    lerp(blury(xi, yi + 1, zi + 1, c), blury(xi + 1, yi + 1, zi + 1, c), xf), yf),
                zf);

    // Normalize
    bilateral_grid(x, y) = interpolated(x, y, 0) / interpolated(x, y, 1);
    Pipeline p({bilateral_grid});

    Var v6, zo, vzi;

    blury.compute_root().split(x, x, v6, 6, TailStrategy::GuardWithIf).split(z, zo, vzi, 8, TailStrategy::GuardWithIf).reorder(y, x, c, vzi, zo, v6).vectorize(vzi).vectorize(v6);
    p.compile_to_module({input}, "bilateral_grid", {Target("host")});
    return 0;
}

compiling gives error:

Internal Error at /home/xuanda/dev/Serializer/Halide/src/IR.cpp:582 triggered by user code at : Condition failed: condition.type().is_scalar(): IfThenElse with vector condition

[abadams]

This compiles fine for me on main. Are you working on an older branch? Maybe one of the other fuzzer bug fixes also fixed this.

[TH3CHARLie]

I work on my branch but merged with the most recent main and most my changes do not touch Halide core, this is kind weird.

[abadams]

Actually my local main was older than I thought. Can repro now. I think this is a new bug, maybe introduced by my last change to vectorization.

[TH3CHARLie]

most likely #7982 i guess

[abadams]

Yeah, that change could easily have changed how powerful loop partitioning is, which is the pass triggering the error.

[abadams]

No, vectorization is producing the following:

      if ((uint1)likely(x8((blury.s0.x.v2.base + 5) <= (((bilateral_grid.extent.0 + bilateral_grid.min.0) + 7)/8)))) {

So I think it's #8093

Either way, shouldn't be too hard to figure out...

[abadams]

Found it. Just a silly mistake I made. I'll open a PR.